Antioxidants

ABSTRACT

ACYL DERIVATIVES OF P-NITROSOPHENOLS, P-NITROSOANILINES AND P-NITROSOPHENYLHYDROXYLAMINES ARE ANTIOXIDANTS FOR RUBBER WHICH ARE RESISTANT TO EXTTRACTION BY SOLVENTS. THE ACYL DERIVATIVES ARE PREFERABLY PREPARED BY ACYLATION AT 10-40*C. IN A WATER-MISCIBLE SOLVENT, BEST IN ADMIXTURE, IN PRESENCE OF A WEAKLY BASIC ACID BINDING AGENT.

United States Patent Offi ce ABSTRACT THE DISCLOSURE Acyl derivatives of p-nitrosophenols, p-nitrosoanilines and p-nitrosophenylhydroxylamines are antioxidants for rubber-"which are resistant to extraction by solvents. The acyl derivatives are preferably prepared by acylation at 1040f C. in a water-miscible solvent, best in admixture, inpre sence of a weakly basic acid binding agent.

-'This invention relatesto the stabilisation of rubbers against-oxidation by the use of acyl derivatives of certain aromatic nitroso compounds.

.p-Nitrosoanilines are of value as antioxidants for rubbers, especially since they are resistant to extraction from the rubberby solventsaTheacyl derivatives used in the present invention have advantages over nitroso anilines in, that-they .aresless ,prone to stain and irritate the skin, they disperse more easilyin the rubber and have less effect on the processing. safety of the rubber.

,,Ac cording tozthe invention there are provided stabilised rubbencompositions containing in stabilising amount an acyl compound which is an, acyl derivative of a nitroso compounmof theformula wherein X is a hydroxyl group or agroup of the formula NHR or-N(OH)R in which R is an alkyl, alkenyl, cycloalkyl or aryl group-or substituted derivative thereof and whereinthe benzene; ring-may optionally be further substituted.

The rubber may be natural rubber or a synthetic rubber for example a polymer orv copolymer derived from a conjugated diene such as cis-polybutadiene, cis-polyisoprene, other polymers of'butadiene or isoprene, polymers Of, 2 -,chlorobutadiene or copolymersof any of the foregoing with each otheror with isobutene, styrene, acrylonitrile, methyl methacrylate, or other well-known polymerisablecompounds.usedinthe manufacture of synthetic rubbers. 9, p i 1- "The-acyl compound may be incorporated into the rubher by any conventional method-For example it may be mixed; onamill .w itl 1 the unvulcanised rubber alone or with othergcompounds used in rubber technology such as vulcanising agents,. sulphur, vulcanising accelerators, retardersantiozohants, other antioxidants, blowing agents, pigments, fillers and waxes. The acyl compounds are of particular value for thestabilisation of vulcanised rubber compositions. 1

Tamount of acylcompoundto be used is convenientlydrom 0.1"t "4.( and preferably from 0.25 to 2. Q%., of.the weight of rubber, Larger or smaller amounts hpyvever..;be;used if. desi red.-

,Theacyl compounds-are derived from the quinone oxime 'o 'r quinone imine oxime tautomers of the nitroso compoundsand have ccmipositionsv of the formulae an acyl group.

isopropyl and n-octyl, alkenyl groups such as oleyl, cy-

cloalkyl groups such as cyclohexyl, aryl groups such as phenyl, p-tolyl and u-naphthyl, and substituted derivatives of the foregoing such as fi-hydroxyethyl, p-hydroxyphenyl and p-chlorophenyl.

The preferred acyl compounds are those derived from nitroso compounds in which X is an alkylamino group, particularly a methylamino or ethylamino group, or an arylamino group, particularly an anilino group.

The acyl group may be derived from an aliphatic, unsaturated aliphatic, cycloaliphatic, aromatic or heterocyclic mono or polycarboxylic acid or substituted derivative thereof. As examples of such acids there are mentioned formic, acetic, lauric, behenic, isobutyric, 3-chloropropionic, l-naphthylacetic, phenoxyacetic, acrylic, oleic, carbonic, alkyl hydrogen carbonic such as ethyl hydrogen carbonic, adipic, azelaic, sebacic, itaconic, cyclobutanoic, cyclohexanoic, cyclodecanoic, naphthenic, cyclohexane- 1,4-dicarboxylic, benzoic, o-, n-, and p-nitrobenzoic, ptoluic, p-chlorobenzoic, l-naphthoic, terephthalic, isophthalic, nicotinic, furoic and quinaldic acids.

In those cases wherein the acyl group is derived from a polycarboxylic acid one or more than one of the carboxylic acid groups may take part in the formation of the acyl compound.

The preferred carboxylic acids from which the acyl groups may be derived are alkane carboxylic acids containing a total of four to eighteen carbon atoms, especially lauric and stearic acids, carbonic acid, alkyl e.g. ethyl hydrogen carbonic acid, u,w-alkanedioic acids containing from six to twelve carbon atoms, especially adipic, azelaic and sebacic acids, and aryl carboxylic acids for example benzoic acid and readily available substituted derivatives thereof such as alkyl, alkoxy or chloro substituted benzoic acids.

The acyl group may alternatively be a 1,3,5-triazinyl group or other heterocyclic group chloro derivatives of which have acylating actions similar to those of acyl chlorides. As examples of such chloroheterocyclic compounds there are mentioned cyanuric chloride, 2,4,5,6 tetrachloropyrimidine and phosphonitrile chlorides. In those cases wherein the chloroheterocyclic compounds contain two or more reactive chlorine atoms one or more of the reactive chlorine atoms may be reacted with the nitroso compound and, if desired, any remaining reactive chlorine atoms may be replaced in conventional manner by reaction with for example amines, alcohols or'phenols.

The acyl group may also be a carbamyl group of the formula R R N.CO wherein R and R are each groups of the type represented by R, especially alkyl groups such as methyl or ethyl or aryl groups such as phenyl.

The acyl group may in addition be derived from an oxyacid of sulphur, phosphorus, silicon or boron. As examples of such acyl groups there arementioned isopropylsulphenyl, benzenesulphenyl, methanesulphonyl, p-toluenesulphonyl, phosphoryl, boryl, silicyl, (RO) O.P-, Cl Si and era-o Ro ,o.P-, ci;si and B- one-1d As optional further substituents in the benzene-ring of the acyl compound there are mentioned alkyl groups such as methyl, ethyl, isopropyl, -n-butyl, isobutyl, terL-butyl, a-methylcyclohexyl, substituted alkyl groups such as benzyl, and aromatic groups such as phenyl. In thosecases Patented July 30, 1974 wherein X is an NHR or N(OH)R group it is preferred that the benzene ring should not be further substituted. When X is an OH group the preferred substituents are alkyl groups, especially 2-isopropyl-5-methyl, 2,5-dimethyl and 3-pentadecyl.

The acyl compounds may be prepared by treating the appropriate nitroso compound of Formula I with preferably an acid chloride but other conventional reactive derivatives of an acid which will give rise to an acyl group, for example an acid anhydride may be used. The reaction is desirably carried out in presence of an acid binding agent, preferably a weakly basic metal compound such as calcium carbonate, calcium hydroxide, sodium bicarbonate and especially sodium carbonate. Other acid binding means can be used, for example caustic alkalis or organic tertiary amines, or the nitroso compounds can be used as preformed metal salts but the former afford less pure products and the latter procedure is inconvenient.

The reaction is desirably carried out in a solvent which may be water or a water-insoluble organic solvent such as toluene or ethyl acetate. The preferred solvents however are water-miscible solvents such as lower aliphatic alcohols such as methanol and especially ethanol, and ketones such as acetone, best results being obtained when these solvents are used in admixture with water, the solvent-water ratio being between about 50:50 and 90:10 by weight. The preferred temperature range using these solvents is from to 40 C.

An additional advantage obtained by use of the preferred process conditions is that the resulting product has greater thermal stability and is more easy to disperse in rubber. For example the benzoyl derivative of 4-nitrosodiphenylamine so prepared is an orange-coloured solid which is essentially stable up to near the melting point of 154-156" C., but when prepared under different conditions the product, which is somewhat greener in shade, may be difiicult to disperse in rubber and may commence to decompose exothermically at up to 40 C. lower.

The product is frequently insoluble in the reaction medium and can be isolated by filtration and washing with water to remove any inorganic salts. If, however, it remains in solution it may be isolated by removal of the solvents by distillation or in suitable cases by precipitation by the addition of water.

The invention is illustrated but not limited by the following Examples in which all parts and percentages are by weight unless otherwise stated.

EXAMPLE 1 10 Parts of 4-nitrosodiphenylamine are dissolved in 125 parts of acetone, and 12.5 parts of anhydrous sodium carbonate are added. The mixture is mechanically stirred, and 5.1 parts of acetic anhydride are added. After a reaction period of 17 hours the mixture is filtered and the filter cake is washed with 100 parts of acetone. The filtrate and washings are poured into 600 parts of water when 11 parts of the required acetyl compound are precipitated. The precipitate is collected and after drying at 50 under reduced pressure it melts at 87-88'C.

Calculated for C H N O.C H O: Carbon, 70.0%, Hydrogen, 5.0% and Nitrogen, 11.7%. Found: Carbon, 70.8%, Hydrogen, 5.1%, and Nitrogen, 11.7%.

EXAMPLE 2 The procedure of Example 1 is repeated using 10 parts of p-toluenesulphonyl chloride in place of the acetic anhydride. There are thus obtained 14.6 parts of the required acyl compound melting at 130-132 C.

Calculated for CmHgNgO-CqHqSOzI Carbon, 64.8%, Hydrogen, 4.54%, Nitrogen, 7.95% and Sulphur, 9.1%. Found: Carbon, 65.5%, Hydrogen, 4.4%, Nitrogen, 7.6% and Sulphur, 8.5%.

4 EXAMPLE 3 10 Parts of 4-nitrosodiphenylamine are dissolved in parts of acetone, and 15 parts of anhydrous sodium carbonate and 6.8 parts of N,N'-dimethylcarbamyl chloride are added. The mixture is stirred and heated under refiux for 30 hours and then filtered. The filter cake is washed with acetone and the filtrate and washings are combined, diluted with water, and warmed under reduced pressure until most of the acetone is evolved and the product precipitates. 6.0 Parts of acyl compound melting at 158160 C., with decomposition, areobtained.

Calculated for C H N O.C H NO: Carbon, 66.9%, Hydrogen, 5.6% and Nitrogen, 15.6%. Found: Carbon, 66.9%, Hydrogen, 5.5% and Nitrogen, 15.9%.

EXAMPLE 4 EXAMPLE 5 The procedure of Example 1 is repeated but using 6.2 parts of ethyl chloroformate as the acylating agent and allowing only 1 hour for the reaction period. 5.3 Parts of acyl compound melting at 8486 C. are obtained.

Calculated for C H N O.C H O Carbon, 66.7%, Hydrogen, 5.2%, and Nitrogen, 10.35%. Found: Carhon, 67.0%, Hydrogen, 5.0% and Nitrogen, 10.5%.

EXAMPLE 6 10 Parts of p-nitrosodiphenylamine are dissolved in parts of acetone and 15 parts of anhydrous sodium carbonate are added. The mixture is stirred and cooled to 0, and a solution of 15 parts of stearoyl chloride in 50 parts of acetone is added dropwise. The mixture is allowed to reach room temperature and stirring is continued for a further hour. The solution is then filtered, and the filter cake is washed with 1000 parts of acetone. Filtrate and washings are combined and diluted with water when 18.6 parts of the acyl compound are precipitated. When dry the melting point is 78-80 C. with decomposition.

Calculated for C H N O-C H O: Carbon, 77.5%, Hydrogen, 9.6% and Nitrogen, 6.0%. Found: Carbon, 78.0%, Hydrogen, 9.6% and Nitrogen, 5.5%.

EXAMPLE 7 10 Parts of 4-nitrosodiphenylamine are dissolved in 100 parts of acetone. 10 Parts of anhydrous sodium carbonate are added, and the mixture is stirred while a solution of 7.3 parts of adipyl chloride in 30 parts of acetone is added. Stirring is continued for 2 hours, and the mixture is then filtered. The filter cake is washed with water to dissolve inorganic salts, and dried, yielding 9.2 parts of acyl compound melting at 159-160 C. with decomposition.

Calculated for (C H N O) C H O Carbon, 71.1%, Hydrogen, 5.2% and Nitrogen, 11.0%. Found; Carbon 70.7%, Hydrogen, 5.5% and Nitrogen, 10.8%.

EXAMPLE 8 The procedure of Example 7 is repeated, but using 7.1 parts of sebacoyl chloride as the acylating agent. 8.9 Parts of acyl compound melting at 136l37 C. are obtained.

Calculated for (C H N O) C H O- Carbon, 72-7%, Hydrogen, 6.1% and Nitrogen, 10.0%. Found: Carbon, 72.6%, Hydrogen, 6.0% and Nitrogen, 9.9%.

6 EXAMPLE 9 EXAMPLE 11 The procedure of Example 7 is repeated using 4.6 Rubber mixes of the following composition are preparts of cyanuric chloride as the acylating agent. 8.6 pared on a two roll mill: Parts of the required acyl compound are obtained.

Calculated for 12 9 2 )2C3N3Cl: Carbon, 63.9%, 5 seokedfiheet Namml Rubber 100 Zinc oxide 3.5 Hydrogen, 3.6% and Chlorine, 6.9%. Found: Carbon, 63 8% H dro en 3 8%and Chlorine 6 3% Steam and 3 y g High abrasion furnace black 45 A L Aromatic process oil 3.5 10 Sulphur 2.5 Rubber mixes of the following composi ion re pr Cyclohexylbenzthiazyl sulphenamide 0.5 pared'by mixing on a two roll mill: Anti id nt 0 or 2 Pale Crepe Natural Rubber 100 The mixes are vulcanised for minutes at 153C. Zinc oxide 10 and the vulcanisates, in sheet form of 0.8 mm. thickness, Stearic acid 1 15 are examined for antioxidant activity as for Example 10. Barium sulphate 75 The results below show the antioxidants of the invention Sulphur 2.5 to lose little of their antioxidant effect after extraction Cyclohexylbenzthiazyl sulphenamide 0.5 and in certain instances the antioxidant eifect is actually Antioxidant As indicated improved.

Benzene Benzoyl Acetyl sulphonyl derivative of derivative of derivative of t-nitrosoe-nitrosm Product 4-nitrosol-mtrosodiphenyldiphenylof exdiphenyldiphenyl- Antioxidant None amine amine ample 2 amine amine Percent on rubber hydrocarbon- 2 2 2 2 2 Time (in hours) for absorption of 2% oxygen:

Unextracted vulcanlsate 11 23 28 17 17 30 Extracted vulcanisate* 8 29 2e 15 15 44 Extracted as described in Example 10.

Norm-The benzene sulphonyl derivative of p-nitrosodiphenylamine is prepared by a procedure similar to that described in Example 2.

The mixes are vulcanised for 20 minutes at 153 C. EXAMPLE 12 and the vulcanisates in sheet form of 0.8 mm. thickness 10 parts of 4-mtrosodrphenylam1ne are dissolved in 100 are examined for antioxidant activity by determining the parts of acetone and 15 parts of anhydrous Sodium time taken in hours for an absorption of 2% of their o weight of yg at C. Mooney Scorch times at bonate are added. The mixture 1s cooled to 0 and stirred. A stream of mtrogen gas contalnmg 5 parts of phosgene 130 C. are measured on the unvulcanised compound a using a Mooney Viscometer The time in minutes (flu) is then bubbled slowly through the mixture. Stirring is required for the Mooney reading to rise ten units above continued for half an after f Q is completethe minimum viscosity is recorded The colour and 8.8 parts of the acyl derivative are precipitated. The prestrength of stain produced by the rubbers in contact with 45 FIPItaIte 1S i; 5 i fg Washed wlth Water- After y g lasticised polyvinyl chloride for 24 hours is assessed 1t me ts at Eisually. Comparable tests are carried out with similar Calculated for (C12H9N20)2C03 Carbml, 71%, and

compounds containing no antioxidant. The results below Hydrogen Found: Carbon: 705%: and Hydrogen show that the antioxidants of the invention have a greater processing safety and stain less compared with 4-nitro- EQMPLE 13 sodiphenylamine and also retain a high proportion of 30 parts of 2,5-dimethyl-4-nitrosophenol are dissolved their antioxidant eiiect after solvent extraction of the in 200 parts of acetone and 25 parts of sodium carbonate vulcanisate. are added. The mixtur' e is stirred and cooled to 0, and a Terephthalie Isophthalic O-acetylacid diester acid diester p-benzo- Product 01- of p-nitrosoof p-nitroso- 4-nitrosoqumone diphenyldiphen'yldiphenyl- Antioxidant None monoxime Example 6 Example 8 Example 7 amine amine amine Percent on rubber hydrocar 2 2 2 2 2 2. Mooney scorching at 130 0.:

tin (minutes) 23 2 Q 17 11 6. Time (in hours) for absorption of 2% oxygen:

Unextracted vulcanisate- 21 32 48 44 52 41 41 52. Extractedvulcanisate" Legssthan 25 41 6 61 25 36 1 40. Contact stain to plasticised PBC- None Light Light Light Light Light Light Intense fawn. reddish greenish greenish brownish greenish yellowish yellow. yellow. yellow. yellow. yellow. brown.

*Aiter 24 hours continuous extraction in a Soxhlet apparatus with a mixture of 110 parts by volume of acetone, 42 parts by volume of methanol and parts by volume of 1,1,1-trichloroethane.

The terephthalic and isophthalic acid diesters of psolution comprising 30 parts of benzoyl chloride and 40 nitroso diphcnylamine used above are prepared by a proparts of acetone is added dropwise. The mixture is alcedure similar to that described in Example 7. lowed to reach room temperature and stirring is continued 7 for a further hour. 150 parts of water are added and the acyl derivative isprecipitated. It is collected and after being washed with water and dried' it'rnelts at 157.

Calculated for C H NO .C H O:, Carbon, 70.6%, Hy-

8 are vulcanised for minutes at 153 C. and the vulcanisates, in sheet formof 0.8 mm. thickness, are examined for antioxidant activity as described in Example 10. The results below show the antioxidants of invention to .lose

70.4%,.Hydrogen, 5.5%, and Nitrogen, 5.7%.

EXAMPLE 14 58 parts of 4-nitrosodiphenylamine areadded to 110 parts of water and 290 parts of ethanol. 36 parts of sodium carbonate are added and the mixture is stirred rapidly at C. 44 parts of benzoyl chloride are added dropwise during minutes. During addition the mixture is cooled to prevent its temperature rising above 30. Stirring is continued for 1% hours. The precipitated benzoyl derivative is then collected, and washed with a little 70% aqueous ethanol and then thoroughly washed with water to remove sodium salts. The yield after drying is 82 parts (93% of theoretical) which melt at 154-156" C.

drogen, 5.1%, and Nitrogen, 5.5%. Found: Carbon, 5 little of their antioxidant activity after extraction.

Laurie Isobutyric n-Hexa- 'n-Butyric acid acid noic acid acid derivaderivaderivaderivative of tive of tive of tive of 4-nitroso- 4-nitroso- 4-nitros0- 4-nitrosodiphenyldiphenyldiphenyldlphenyl- Antioxidant None amine amine amine amine Percent on rubber hydrocarbon 2 2 2 2 Time (in hours) for absorption of 2% oxygen:

Unextraeted vulcanisate 18 36 39 38 41 Extracted vulcanisate 8 33 36 34 The acyl derivatives used above are prepared by reacting 4-nitrosodiphenylamine with lauryl chloride and isobutyric chloride respectively by the procedure of Example 6, and with n-hexanoic anhydride and n-butyric anhydride respectively by the procedure of Example 1.

EXAMPLE 17 Benzoyl 3-ChloropChloroderivative propionyl benzoyl of derivative derivative Benzoyl -nitroso- Product of of derivative 2-isopro- Product of 4 -nitroso- 4-mtrosopy1-5- of example drphenyldiphenyl- 4-nitrosomethyl example Antioxidant None 13 amine amine phenol phenol 9 Percent on rubber hydrocarbon 2 2 2 2 2 2 Time (in hours) for absorption 011% oxygen:

Unextracted vulcanisate- 14 23 28 32 21 13 25 Extracted vuleanisate 4 9 24 22 18 8 30 The product 1s obtained 1n the form of fine orange- We claim:

yellow crystals and can easily be dispersed in rubber. A 10 g. sample when heated at a temperature rising by 2 C. per minute decomposes at a temperature above 143 C. This compound, when obtained by benzoylation under materially different conditions is slightly greener in shade, is not so easily dispersed in rubber, and similarly heated, decomposes exothermically at a temperature which may be as low as 107 C.

EXAMPLE 15 Product Product of examof exam- Antioxidant None ple 5 ple 12 Percent on rubber hydrocarbon. 2 2 Time (in hours) for absorption 01 1% oxygen:

Unextraeted vuleanisate--- 9 15 31 Extracted vnlcanisate. 4 13 33 EXAMPLE 16 Rubber mixes are prepared by the procedure of Example 0 usin the antioxidants listed below. The mixes wherein X is a group of the formula NHR in which R is an alkyl, alkenyl, cycloalkyl, aryl, p-hydroxyphenyl or pchlorophenyl group, the acyl group being derived from alkane carboxylic acids containing 4 to 18 carbon atoms, a,w-alkane-dicarboxylic acids containing 6 to 12 carbon atoms, aryl monoor di-carboxylic acids or alkyl, alkoxy or chloro derivatives thereof.

2. Stabilised rub'ber compositions as claimed in Claim 1 wherein X is a group NI-IR in which R is an aryl group.

3. Stabilised rubber compositions as claimed in Claim 1 wherein R is a phenyl group.

4. Stabilised rubber compositions as claimed in Claim 1 wherein the acyl group is a benzoyl group.

5. Stabilised rubber compositions as claimed in Claim 1 wherein the amount of acyl compound is from 0.1 to 4.0% of the weight of rubber.

6. Stabilised rubber compositions as claimed in Claim 1 wherein the amount of acyl compound is from 0.25 to 2.0% of the weight of rubber.

(References on following page) 9 10 References Cited DONALD E. CZAJA, Primary Examiner UNITED STATES PATENTS w. E. PARKER, Assistant Examiner 2,395,937 7/1959 Baldwin 260-415 3,309,373 3/1967 Danzig 260--78l 3,384,613 5/1968 Parks 260-459 R 5 260-415, 404, 557, 781

I JN TTID STATES PATENT OFFJIICE I CERTIFKCATBE OF CORRECTION a lnv n fifi fir igp Thmggg shworth, Kenneth Crawford. and

Peter Michael Quan Y It is certified that error appears in the above-identified patent and thatsaid Letters Patent are hereby corrected as shownbelow:

Column 1, in the heading please insertthe priority as follows: -Claims priority, application 7 I Great Britain 5667/71 filed March 1, 1971-- Signed and sealed this 29th day of October 1974.

(SEAL) Attest: 3

McCOY M. GIBSON-JR. C. MARSHALL DANN Attesting Officer Commissioner of Patents 

